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Beyond the beam : evaluation and application of handheld X-ray fluorescence in archaeology

(2015)
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(UGent) , (UGent) and (UGent)
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Abstract
The starting point of this project was to bridge the gap between the Departments of Analytical Chemistry and Archaeology. Archaeology has evolved from a more historically and art-historically orientated field of research to a fully emancipated science, comfortably adopting GIS, 3D modelling and chemical analysis to serve its own needs. The rapidly evolving field of XRF (X-ray fluorescence) analysis and the development of a new generation of lightweight, high-performance handheld XRF analysers promised new possibilities for in situ elemental determination. The primary aim of this research project was to evaluate the applicability of such a handheld XRF analyser when used in archaeological contexts and to develop a comprehensible protocol for data-processing. To fulfil these objectives, the Olympus Innov-X handheld XRF analyser was obtained and characterised and a work methodology was developed applying established lab protocols used in analytical chemistry. This instrument was then employed in three archaeological case studies where it investigated respectively the provenance of post-medieval Flemish stove-tiles, the origin and distribution of Iron Age red-painted pottery from Mount Kemmel and related sites, and the geochemical composition of archaeological soil features in the Yustyd valley (Russia) during excavations in 2011. The research combined different XRF techniques, with a central role for handheld XRF spectrometry in all selected archaeological applications. In addition, the measurements of both µ-XRF (micro-XRF) and TXRF (Total Reflection XRF) were used to act as a point of reference for the handheld measurements, since reference materials for the archaeological materials under focus are not available, and Raman spectroscopy was used to characterize the pigment in the red-painted pottery. Methodology and characterization of handheld XRF analysers The first part of this thesis consists of three chapters which deal with X-ray fluorescence in general and the instrumentation and methodology that were used in this work. These chapters serve as an introduction to and point of reference for the rest of the thesis. Chapter 1 (Introduction) introduces the research and provides a broader context by placing it in the general evolution of XRF analysis in archaeology and by discussing current issues concerning the validity of handheld XRF. The chosen research strategy and the aims and objectives of this research are also discussed. Chapter 2 (Methodology) provides an overview of the instrumentation that was used in this research and the sample preparation and data processing techniques that were applied per instrument and project. The methodology is applicable to the three archaeological test cases. Chapter 3 (Evaluation of commercial handheld XRF: selecting the right tool for archaeological research) describes the evaluation of six commercially available handheld XRF analysers. The instruments are tested on their performance, stability and ease of use, using a set of standard reference materials and archaeological applications. The characterization of the Olympus Innov-X Delta handheld XRF analyser is another focus of this chapter. The characterization is essential for understanding the potential of the instruments, interpreting the results and configuring an ideal set-up. In the field. The application of hXRF in archaeological research projects In part 2 of the thesis, the hXRF analyser is taken into the field, where it is confronted with three archaeological test cases (Chapters 4-6). The first application is the archaeological and archaeometrical investigation of two ‘virtual dwellings’ in the Yustyd valley (Altai Republic, Russian Federation). In the summer of 2011, two Bronze Age geometric stone settings of the type ‘virtual dwelling’ were excavated by Belgian and Russian archaeologists in the Yustyd valley in the Altai mountains. During this campaign, handheld XRF analysis was used to perform a geochemical survey of the excavated structures in order to see if the soil features, as encountered during excavation, had a different chemical composition than the surrounding soil and if their composition could be attributed to a specific use of the monuments. Soil samples were taken to be further investigated by means of TXRF spectroscopy, a technique with very low detection limits often used for the ultra-trace analysis of particles. Even though we strongly believe in the potential of hXRF for geoarchaeological survey, the results for this study were rather limited. Possibly the harsh environmental conditions and barren soil influenced the results and their interpretation. Another factor might be the archaeological site itself: it is possible that the impact of the activities on the site, some four millennia ago, was too limited to leave traces today. The archaeological levels on the site not only appear to be featureless, but might have been so in origin. Any ritual, funerary or day-to-day use of the sites might have been minimal and not detectable by the chosen XRF technique. Chapter 5 presents the second and most extensive case study: an archaeometrical investigation of Flemish late and post-medieval stove-tiles by means of hXRF and µ-XRF. Stove-tiles are no uncommon goods in Flemish excavations, their origin, however, is unknown since no pottery workshops with evidence of stove-tile production have been found in excavation. The combination of these techniques was used to determine the chemical composition of these tiles and by comparison with locally produced pottery and raw clay, to determine their provenance. Furthermore, the impact of tile-stoves and their imagery as a symbol of status and a representation of identity was discussed and interpreted in relation to the archaeometrical results. The hXRF analyses of the whiteware stove-tiles delivered consistent results showing well-defined groups within the research material, corroborating with the results of the µ-XRF analysis. The study clearly set the whiteware stove-tiles apart from the Antwerp maiolica: either the tiles are imported as a finished product, or the clay was imported and locally used for stove-tile production. The results of the redware stove-tiles on the other hand were more complex. The hXRF results diverged considerably from those of the µ-XRF analysis, giving a completely different view on the relation between the comparative material and the stove-tiles themselves. For now, this divergence is explained by the difference between the two XRF techniques and the detailed measurements that can be taken with the µ-XRF instrument as opposed to the larger beam size of the hXRF instrument and the interference of exterior contamination that is inevitable with handheld XRF. The third and last case study (Chapter 6) covers a provenance-study of Iron Age red-painted pottery. The goal was to investigates whether the red-painted pottery, found on several Iron Age sites in Belgium and Northern France and referred to as Kemmelware, was actually produced in the Mount Kemmel hill fort. hXRF was employed to determine the elemental composition of the pottery while Raman spectroscopy was used to investigate the pigment used for the red slip decorations. The investigation proved very interesting, as the hXRF data clearly demonstrated connections between the Iron Age settlement of Mount Kemmel and those of Kooigembos, Houplin-Ancoisne and Elversele, which can support the hypothesis that the pottery was produced in Kemmel and then distributed to other Iron Age sites. The Houplin-Ancoisne dataset gave evidence of two types of red-painted pottery: one group clearly diverged from the Kemmelware and can be labelled as locally produced red-painted pottery. The pottery from Hove was also chemically and technologically different, again indicating local production. Since only a limited number of sites were investigated, it would be interesting to extend the research with material from other Iron Age settlements, especially from sites in northern France. That way, it might be possible to further delineate the area where the influence of Mount Kemmel is perceptible. Conclusions, future perspectives and final thoughts By now it is clear that there is no such thing as easy answers where chemical analysis of archaeological samples is concerned. It is, however, through extensive application that we can further develop a methodology that allows us to limit the unknown factors that are always present when working with very heterogeneous materials as ceramics and soils. Only by using a lab protocol – also when working in the field –, by attentive monitoring of the data acquisition and by following predetermined steps of data processing, qualitative data can be obtained. In order for hXRF to become fully integrated in archaeology, it must be stressed that archaeologists need to understand the science behind XRF spectrometry and data processing in order to correctly evaluate the produced results and to translate them into an archaeological interpretation. Moreover, knowledge of the chemical process and the composition and variability of archaeological materials will prove indispensable in formulating the most successful research strategies. We hope that this contribution has been a step forwards for a true integration of hXRF into archaeology. In contrast to applying hXRF as a fancy technique because of its publication possibilities, this true integration implies the correct application of hXRF using the protocols and knowhow developed by analytical chemistry and implementing it in an archaeological manner. True integration also means that hXRF analysis in archaeology must not be seen as the sole purpose of a research, but rather as the means to answering well determined archaeological research questions.
Keywords
Altai, Kemmel, Flanders, red-painted pottery, stove-tiles, X-ray fluorescence, archaeology, µ-XRF spectroscopy, handheld XRF analysis, hXRF

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Citation

Please use this url to cite or link to this publication:

MLA
De Langhe, Kaatje. “Beyond the Beam : Evaluation and Application of Handheld X-ray Fluorescence in Archaeology.” 2015 : n. pag. Print.
APA
De Langhe, K. (2015). Beyond the beam : evaluation and application of handheld X-ray fluorescence in archaeology. Ghent University. Faculty of Arts and Philosophy, Ghent, Belgium.
Chicago author-date
De Langhe, Kaatje. 2015. “Beyond the Beam : Evaluation and Application of Handheld X-ray Fluorescence in Archaeology”. Ghent, Belgium: Ghent University. Faculty of Arts and Philosophy.
Chicago author-date (all authors)
De Langhe, Kaatje. 2015. “Beyond the Beam : Evaluation and Application of Handheld X-ray Fluorescence in Archaeology”. Ghent, Belgium: Ghent University. Faculty of Arts and Philosophy.
Vancouver
1.
De Langhe K. Beyond the beam : evaluation and application of handheld X-ray fluorescence in archaeology. [Ghent, Belgium]: Ghent University. Faculty of Arts and Philosophy; 2015.
IEEE
[1]
K. De Langhe, “Beyond the beam : evaluation and application of handheld X-ray fluorescence in archaeology,” Ghent University. Faculty of Arts and Philosophy, Ghent, Belgium, 2015.
@phdthesis{6715561,
  abstract     = {The starting point of this project was to bridge the gap between the Departments of Analytical Chemistry and Archaeology. Archaeology has evolved from a more historically and art-historically orientated field of research to a fully emancipated science, comfortably adopting GIS, 3D modelling and chemical analysis to serve its own needs. The rapidly evolving field of XRF (X-ray fluorescence) analysis and the development of a new generation of lightweight, high-performance handheld XRF analysers promised new possibilities for in situ elemental determination. The primary aim of this research project was to evaluate the applicability of such a handheld XRF analyser when used in archaeological contexts and to develop a comprehensible protocol for data-processing. 
To fulfil these objectives, the Olympus Innov-X handheld XRF analyser was obtained and characterised and a work methodology was developed applying established lab protocols used in analytical chemistry. This instrument was then employed in three archaeological case studies where it investigated respectively the provenance of post-medieval Flemish stove-tiles, the origin and distribution of Iron Age red-painted pottery from Mount Kemmel and related sites, and the geochemical composition of archaeological soil features in the Yustyd valley (Russia) during excavations in 2011. The research combined different XRF techniques, with a central role for handheld XRF spectrometry in all selected archaeological applications. In addition, the measurements of both µ-XRF (micro-XRF) and TXRF (Total Reflection XRF) were used to act as a point of reference for the handheld measurements, since reference materials for the archaeological materials under focus are not available, and Raman spectroscopy was used to characterize the pigment in the red-painted pottery.
Methodology and characterization of handheld XRF analysers
The first part of this thesis consists of three chapters which deal with X-ray fluorescence in general and the instrumentation and methodology that were used in this work. These chapters serve as an introduction to and point of reference for the rest of the thesis. Chapter 1 (Introduction) introduces the research and provides a broader context by placing it in the general evolution of XRF analysis in archaeology and by discussing current issues concerning the validity of handheld XRF. The chosen research strategy and the aims and objectives of this research are also discussed. Chapter 2 (Methodology) provides an overview of the instrumentation that was used in this research and the sample preparation and data processing techniques that were applied per instrument and project. The methodology is applicable to the three archaeological test cases. Chapter 3 (Evaluation of commercial handheld XRF: selecting the right tool for archaeological research) describes the evaluation of six commercially available handheld XRF analysers. The instruments are tested on their performance, stability and ease of use, using a set of standard reference materials and archaeological applications. The characterization of the Olympus Innov-X Delta handheld XRF analyser is another focus of this chapter. The characterization is essential for understanding the potential of the instruments, interpreting the results and configuring an ideal set-up.
In the field. The application of hXRF in archaeological research projects
In part 2 of the thesis, the hXRF analyser is taken into the field, where it is confronted with three archaeological test cases (Chapters 4-6). The first application is the archaeological and archaeometrical investigation of two ‘virtual dwellings’ in the Yustyd valley (Altai Republic, Russian Federation). In the summer of 2011, two Bronze Age geometric stone settings of the type ‘virtual dwelling’ were excavated by Belgian and Russian archaeologists in the Yustyd valley in the Altai mountains. During this campaign, handheld XRF analysis was used to perform a geochemical survey of the excavated structures in order to see if the soil features, as encountered during excavation, had a different chemical composition than the surrounding soil and if their composition could be attributed to a specific use of the monuments. Soil samples were taken to be further investigated by means of TXRF spectroscopy, a technique with very low detection limits often used for the ultra-trace analysis of particles. Even though we strongly believe in the potential of hXRF for geoarchaeological survey, the results for this study were rather limited. Possibly the harsh environmental conditions and barren soil influenced the results and their interpretation. Another factor might be the archaeological site itself: it is possible that the impact of the activities on the site, some four millennia ago, was too limited to leave traces today. The archaeological levels on the site not only appear to be featureless, but might have been so in origin. Any ritual, funerary or day-to-day use of the sites might have been minimal and not detectable by the chosen XRF technique.
Chapter 5 presents the second and most extensive case study: an archaeometrical investigation of Flemish late and post-medieval stove-tiles by means of hXRF and µ-XRF. Stove-tiles are no uncommon goods in Flemish excavations, their origin, however, is unknown since no pottery workshops with evidence of stove-tile production have been found in excavation. The combination of these techniques was used to determine the chemical composition of these tiles and by comparison with locally produced pottery and raw clay, to determine their provenance. Furthermore, the impact of tile-stoves and their imagery as a symbol of status and a representation of identity was discussed and interpreted in relation to the archaeometrical results. The hXRF analyses of the whiteware stove-tiles delivered consistent results showing well-defined groups within the research material, corroborating with the results of the µ-XRF analysis. The study clearly set the whiteware stove-tiles apart from the Antwerp maiolica: either the tiles are imported as a finished product, or the clay was imported and locally used for stove-tile production. The results of the redware stove-tiles on the other hand were more complex. The hXRF results diverged considerably from those of the µ-XRF analysis, giving a completely different view on the relation between the comparative material and the stove-tiles themselves. For now, this divergence is explained by the difference between the two XRF techniques and the detailed measurements that can be taken with the µ-XRF instrument as opposed to the larger beam size of the hXRF instrument and the interference of exterior contamination that is inevitable with handheld XRF.
The third and last case study (Chapter 6) covers a provenance-study of Iron Age red-painted pottery. The goal was to investigates whether the red-painted pottery, found on several Iron Age sites in Belgium and Northern France and referred to as Kemmelware, was actually produced in the Mount Kemmel hill fort. hXRF was employed to determine the elemental composition of the pottery while Raman spectroscopy was used to investigate the pigment used for the red slip decorations. The investigation proved very interesting, as the hXRF data clearly demonstrated connections between the Iron Age settlement of Mount Kemmel and those of Kooigembos, Houplin-Ancoisne and Elversele, which can support the hypothesis that the pottery was produced in Kemmel and then distributed to other Iron Age sites. The Houplin-Ancoisne dataset gave evidence of two types of red-painted pottery: one group clearly diverged from the Kemmelware and can be labelled as locally produced red-painted pottery. The pottery from Hove was also chemically and technologically different, again indicating local production. Since only a limited number of sites were investigated, it would be interesting to extend the research with material from other Iron Age settlements, especially from sites in northern France. That way, it might be possible to further delineate the area where the influence of Mount Kemmel is perceptible.
Conclusions, future perspectives and final thoughts
By now it is clear that there is no such thing as easy answers where chemical analysis of archaeological samples is concerned. It is, however, through extensive application that we can further develop a methodology that allows us to limit the unknown factors that are always present when working with very heterogeneous materials as ceramics and soils. Only by using a lab protocol – also when working in the field –, by attentive monitoring of the data acquisition and by following predetermined steps of data processing, qualitative data can be obtained. In order for hXRF to become fully integrated in archaeology, it must be stressed that archaeologists need to understand the science behind XRF spectrometry and data processing in order to correctly evaluate the produced results and to translate them into an archaeological interpretation. Moreover, knowledge of the chemical process and the composition and variability of archaeological materials will prove indispensable in formulating the most successful research strategies. 
We hope that this contribution has been a step forwards for a true integration of hXRF into archaeology. In contrast to applying hXRF as a fancy technique because of its publication possibilities, this true integration implies the correct application of hXRF using the protocols and knowhow developed by analytical chemistry and implementing it in an archaeological manner. True integration also means that hXRF analysis in archaeology must not be seen as the sole purpose of a research, but rather as the means to answering well determined archaeological research questions.},
  author       = {De Langhe, Kaatje},
  keywords     = {Altai,Kemmel,Flanders,red-painted pottery,stove-tiles,X-ray fluorescence,archaeology,µ-XRF spectroscopy,handheld XRF analysis,hXRF},
  language     = {eng},
  pages        = {XXVI, 308},
  publisher    = {Ghent University. Faculty of Arts and Philosophy},
  school       = {Ghent University},
  title        = {Beyond the beam : evaluation and application of handheld X-ray fluorescence in archaeology},
  year         = {2015},
}